Selection Problems with Converting Quads to Tris in Game Engine?
Running bpy.ops operators in the game engine wont work well (if at all),

Best have the triangulated mesh on a hidden layer, and swap in the triangulated mesh when you need it.

Note, if you really wanted you could use LibLoad to convert a mesh while the game runs, and you could also use bmesh to triangulate the mesh, but this is fairly advanced API use, and Id not really recommend it since it wont work in the blender player.